Psychologists are putting it down to nostalgia, while pragmatists say it's the credit crunch. But whatever the reason, sales of part-baked bread have doubled in the past year.

Tesco says its part-baked bread sales have risen 47 per cent, while Asda has seen a 60 per increase. Asda attributes the rise to the increased trend for staying in to save money. 'People are cooking for themselves more and cooking for friends. Part-baked is a cheat's way to serve piping hot, fresh bread,' said a spokesman.

Tesco believes there is a deeper reason and drafted in a scientist to explain it. During a time of insecurity and uncertainty, it's all apparently down to the 'Proust effect', named after the 19th-century French author who suggested that the rich, heady smell of baking bread created feelings of nostalgia for mum's kitchen and an instant sense of homeliness.

'Freshly baked bread emits quite a sweet smell,' said Dr Martin Corbett, an expert in the science of smell at Warwick University. 'It so happens that sweet smells are almost universally perceived by people as pleasant and therefore the likelihood of triggering happy memories is greatly increased.'

Even the stalling housing market could be playing a part, said Tesco's bakery category director, Stephen Mason. 'It's a well known fact that one of the best ploys if you want to sell your home is to have bread baking in the kitchen.'